Overturned big rigs are playing havoc with Houston area traffic Thursday morning.

The latest mishap occurred about 8:40 a.m. on the outbound Northwest Freeway near Beltway 8.

Officials said when the tractor-trailer toppled over, it hit and damaged the barrier between the main lanes and the HOV lane. Three lanes were blocked while crews cleared the scene.

The other 18-wheeler flipped about 6:20 a.m. on the frontage road of the inbound Katy Freeway near Highway 99. Officials said the two frontage lanes would likely be blocked until about noon while crews cleared the scene.

No information was available about possible injuries or what caused the wrecks.